The present invention relates to a storage device that performs a rebuild process and a rebuild process method for a storage device.
A storage device in which a plurality of magnetic disk devices are used for redundant storage of data is known. In the case where one magnetic disk device has failed in such a storage device, a process of logically disconnecting that failed magnetic disk device is performed. Then, the storage device continues operation in a degraded state without redundancy using the remaining magnetic disk devices that have not failed.
In order to restore the storage device operating in the degraded state in this manner to a state with redundancy, a user needs to detach the failed magnetic disk device from the storage device and attach a new magnetic disk device to the storage device. When the new magnetic disk device is attached in this manner, the storage device executes a rebuild process of storing rebuilt data in the newly attached magnetic disk device. When the rebuild process is finished, the storage device is restored to a state with redundancy.
Also, a known example of disk array devices in which a plurality of magnetic disk devices are used for redundant storage of data increases the speed of writing data by enabling a write cache of a hard disk device with high disk access frequency (for example, see Patent Document 1).
Patent Document 1: Patent Publication JP-A-2000-305717
In a conventional storage device, the already-mentioned rebuild process is performed in parallel with a process relating to access to the magnetic disk device in normal usage. Therefore, there is a possibility that many writes to the newly attached magnetic disk device reduces the performance of a system including the storage device.
In order to prevent such a reduction in performance of the system, it is conceivable to set in advance an interrupt rate of the rebuild process with respect to the process relating to access to the magnetic disk device in normal usage.
However, in the case where the interrupt rate of the rebuild process is set to be small, the performance of the system including the storage device is not reduced, but the execution time of the rebuild process becomes longer. Therefore, time in which the storage device operates in the degraded state becomes longer, and the possibility of a system breakdown due to occurrence of a failure of the new magnetic disk device becomes higher.
On the other hand, in the case where the interrupt rate of the rebuild process is set to be high, the execution time of the rebuild process becomes shorter, but the possibility that the performance of the system including the storage device is reduced becomes higher.
That is, with a method of setting the already-mentioned interrupt rate, problems of the reduction in performance of the system including the storage device and an increase in time of the rebuild process cannot be solved together.
Also, by applying a technique of Patent Document 1 to enable the write cache of a newly attached magnetic disk device, it is possible to increase the speed of writing to that magnetic disk device. Therefore, by utilizing the technique of Patent Document 1, it may seem that achieving an increase in the speed of the rebuild process without reducing the performance of the system including storage device is possible.
However, there is a risk of losing data on the write cache when a state of power discontinuity occurs in the storage device due to an unexpected fault during the rebuild process. In the case where the data on the write cache is lost in this manner, the storage device can no longer distinguish which address the rebuild process has been finished up to. Therefore, after power is restored, it is conceivable that there arises a need for the storage device to perform an inefficient process such as, for example, starting the rebuild process over.